I have never heard of problems related to PET base with continuous transport processors.
Furthermore DR5chrome state that they use for E-6 processors from italian Technolab. To my understanting they only made film processors of the dip-and-dunk principle.

Neither have I, but if someone is rufusing to develop PET films they must be worried about something. BTW isn't this Dwanes we are talking about not DR5?

I don't know if this could be an issue but I remember a processor that had IR film sensors at the edge for repeleshment if PET is used they might have a light pipe issue.
Unlikely though- I think Dwanes are being Über careful.

EDit I think Fleath had the best explaination, the most logical one anyhow.